NOMA and Coded Multicasting in Cache-Aided Wireless Networks

Coded multicasting is considered to be an effective approach to simultaneously serve multiple users in the same frequency/time/code resource, which is made possible by exploiting the information available in users’ caches. Recently, non-orthogonal multiple access (NOMA) has emerged as an alternative transmission technique for cache-aided network. In cache-aided NOMA system, cache-enabled interference cancellation (CIC) is employed to cancel the interference using the information in the cache, and thus enhance the user transmission rate, particularly for the weak users. Despite the enhanced spectral efficiency offered by both techniques, complexity issue arises from handling large number of users. Therefore, user pairing/clustering should be employed to limit the number of users served in the same time-frequency resource. However, the key question is which delivery technique performs better under different pairing scenarios. In this paper, the performance of NOMA and coded multicasting for two-user pairing are investigated in terms of probability of sum rate comparison and outage probability. In order to exploit the benefits of NOMA and coded multicasting, we also propose a hybrid delivery scheme, which select either NOMA or coded multicasting depending on the channel conditions of the paired users in each resource block (RB). A joint mode selection, power allocation and user pairing scheme is developed to enhance the performance of the hybrid scheme. Both analytical and simulation results demonstrate that NOMA outperforms coded multicasting when pairing users whose channel gains are highly distinctive, while coded multicasting is preferred when the paired users have similar channel gains. In addition, the hybrid scheme is demonstrated to offer enhanced sum rate performance in comparison to NOMA and coded multicasting.